Graphic arts process simulator modified for letterpress simulation

ABSTRACT

Disclosed is an improved graphic arts process simulator, which enables accurate simulation of a letterpress graphic arts process. Existing graphic arts process simulators generally include an analog signal processor in which various signal processing elements are used to process an electrical signal representative of a halftone transparency in accordance with the steps of a selected graphic arts process. The improvement described herein is a modified analog signal processor which simulates nonuniformities that normally occur in a letterpress graphic arts process and more specifically simulates the dot etch loss which normally occurs when a printing plate for letterpress printing is made from such a halftone transparency.

United States Patent [191 Page Mar. 26, 1974 GRAPHIC ARTS PROCESSSIMULATOR MODIFIED FOR LETTERPRESS SIMULATION [75] Inventor: Charles E.Page, Westbury, NY.

[73] Assignee: Hazeltine Corporation, Greenlawn,

[22] Filed: Nov. 16, 1972 [21] Appl. No.: 307,326

[52] U.S. Cl ..178/6, 178/5.2 R, 178/6.6 B, l78/6.7 R [51] Int. Cl. H04n7/18 [58] Field of Search 178/5.2 A, 5.2 R, 6.7 R, l78/6.6 B

[56] References Cited UNITED STATES PATENTS 3,128,333 4/1964 Loughlin178/5.2 A

Primary Examiner-Howard W. Britton [5 7] 1 ABSTRACT Disclosed is animproved graphic arts process simulator, which enables accuratesimulation of a letterpress graphic arts process. Existing graphic artsprocess simulators generally include an analog signal processor in whichvarious signal processing elements are used to process an electricalsignal representative of a halftone transparency in accordance with thesteps of a selected graphic arts process. The improvement describedherein is a modified analog signal processor which simulatesnonuniformities that normally occur in a letterpress graphic artsprocess and more specifically simulates the dot etch loss which normallyoccurs when a printing plate for letterpress printing is made from sucha halftone transparency.

3,123,666 3/1964 Bailey 178/5.2 A 3 Claims, 4 Drawing Figures I 0 norETCH STROKE INK HALF-TONE MODE Loss ADJUST SPREAD SIGNAL S'MULATOR ISELECTOR SIMULATOR SIMULATOR SIMULATOR 'NVERTOR 1 l I l6 I5 I l GRAPHICARTS PROCESS SIMULATOR MODIFIED FOR LETTERPRESS SIMULATION CROSSREFERENCE TO RELATED APPLICATIONS This invention refers to andincorporates by reference the material disclosed in copendingapplication Ser. No. 242,867, entitled Graphic Arts Process SimulationSystem, filed Apr. 10, 1972, and assigned to the same assignee as theinstant application, which in turn, is a continuation of applicationSer. No. 874,550 entitled Graphic Arts Process Simulation System, filedNov. 6, 1969 and now abandoned.

In the above-mentioned copending application there is described a systemwhich simulates a graphic art process so that the appearance of thefinal color print, which will result from that process, can be predictedbefore the expensive and time-consuming task of manufacturing printingplates is undertaken. In this and other graphic arts process simulatorsthere is generally included electronic circuitry which simulates varioussteps in the printing process. In the copending application thiscircuitry is located in a portion of the apparatus called the firstanalog signal processor. This processor first develops an electricalsignal representative of a halftone transparency and thenprocesses thissignal in accordance with electronic analogs of the actual steps in aselected graphic arts process to provide output signals which arerepresentative of the actual areas of ink which would be deposited onpaper by a printing plate made from that transparency.

In the analog processor of the copending application this last step isaccomplished by a printing simulator, which consists of several signalprocessing elements each of which has a transfer characteristic thatcorresponds to a particular step in the actual printing process. Theprinting simulator, therefore, has an overall transfer characteristicwhich represents the relation ship between dot area on the halftonetransparency and the corresponding dot area of ink actually deposited onpaper by a printing plate made from that transparency.

The above-mentioned printing simulator assumes that the process ofmanufacturing a printing plate from a halftone transparency is accurateso that dot area on the printing plate is equal to the corresponding dotarea on the halftone transparency. This is, in fact, the case in anoffset printing process and thus the abovedescribed apparatus is anaccurate. simulation ,of this process. In letterpress printing, however,the printing plates do not accurately depict the halftone from whichthey are made. Specifically, a letterpress printing plate is made bycoating a copper plate with a photoresist material. The photoresist isthen exposed to light through the halftone transparency, creating apattern on the photoresist representative of the transparency. Dependingon the type of photoresist used, either exposed or unexposed areas ofthis pattern are protected from the action of etching solutions. Thus,the pattern is transferred to the copper plate by applying anappropriate etching solution to etch away unprotected areas of copper.However the etching process is not easily controlled and even protectedareas of the copper are sometimes partially etched away. This dot etchloss may be as great as 20 percent of the protected areas, causingsmaller dots to be completely etched away and larger dots to be etchedin part. The result is a washingout effect on the actual print made fromthe plate, such that certain tones appear somewhat lighter than theywould if the printing plate accurately represented the halftonetransparency from which it was made. Since prior art graphic artsprocess simulators do not take this defect into account, theirprediction of the appearance of the actual color print will not reflectits true appearance.

It is, therefore, an object of this invention to provide an analogsignal processor which simulates the dot etch loss that occurs whenletterpress printing plates are made.

It is a further object of this invention to provide such an analogprocessor by inexpensively modifying exist ing analog signal processorssuch as the type described in the referenced copending application.

SUMMARY OF THE INVENTION A graphic arts process simulator which includesan analog signal processor wherein there is processed an electricalsignal representative of the halftone transparency from which a printingplate is made; in accordance with the invention there is provided animproved analog signal processor capable of simulating a letterpressgraphic arts process. The improvement comprises a signal processingelement responsive to the electrical signal and having a transfercharacteristic proportional to the dot etch loss which normally occurswhen letterpress printing plates are made.

For-a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION AND OPERATION OF THEINVENTION In FIG. 1 there is shown an analog signal processor 10 of thetype described in the aforementioned copending application but modifiedto include the present invention. As previously stated, the analogprocessor ac-v cepts signals representative of a transparency from whicha printing plate is to be made, and processes the signal in accordancewith various steps in the graphic arts process in order to provideoutput signals from which the appearance of an actual color print can bepredicted. It will be recognized that the analog processor may consist.of either three or four identical channels in order to simulate athree-color or a four-color printing process. However, only one channelis illustrated in FIG. 1 for clarity and convenience.

Briefly, the input signal to the analog signal processor is a signalrepresentative of either a continuous-tone or a halftone transparencyfrom which it is desired to make a printing plate. If the input signalrepresents a continuous-tone transparency, halftone simulator 11 is usedto simulate the screening process which will convert the continuous-tonetransparency to a halftone transparency. Halftone simulator 11 can beby-passed by mode selector 12 if the input signal already represents ahalftone transparency.

Stroke adjust simulator l3, ink-spread simulator 14, and signal inverter15 are signal processing elements which together comprise the printingsimulator of the copending application. The function of these signalprocessing elements is to accept a signal representative of a halftonetransparency and process it in accordance with the steps of the actualprinting process. For example, ink-spread simulator l4 simulates thetendency of ink deposited on paper to spread to a larger area than itoccupied on the printing plate itself. More detailed descriptions of thestructure and operation of the above element can be found in thedescriptions of likeentitled elements in the copending application.

Up until now what has been described is substantially identical to theanalog processor of the referenced copending application and if anoffset graphic arts process were to be simulated, in which the printingplate is substantially identical to the halftone transparency from whichit is made, the processor would be an accurate analog of that printingprocess. However, in a letterpress process, the printing plates do notaccurately reflect the halftone transparencies from which they are made.As described hereinabove, there is a substantial and undesirable etchingaway of protected areas of the printing plate (dot etch loss) whichcauses complete loss of small dots and partial loss of larger dots.

In order to simulate this dot etch loss, element 16 is included inanalog signal processor 10 at a point in the signal path where thereexists an electrical signal representative of the halftone transparencyfrom which the printing plate is to be made. Also included in processor10 is a by-pass switch 17, which can be used to effectively remove dotetch loss simulator 16 from the signal path, when letterpress operationis not being simulated.

Simulator 16 is a signal processing element, for example a nonlinearamplifier, whose transfer characteristic is selected to be proportionalto the dot etch loss involved. The amount of dot etch loss depends uponthe particular etching solution, photoresist, and printing plate used,and can be easily ascertained by experimentation. Since this loss isessentially uniform over the area of the printing plate, with small dotsbeing completely eliminated and larger dots being partially eliminated,once the amount of loss is determined, an amplifier having anappropriate transfer characteristic can be easily designed. Thus, simplystated, dot etch loss can be simulated by including a nonlinearamplifier, having a transfer characteristic representative of the loss,within analog signal processor 10, at a point in the circuit where theelectrical signal is representative of the halftone transparency.

The above-described embodiment has several advantages in that it uses anindependent signal processing element 16 to simulate dot-etch loss, andthus continues the one-for-one correspondence, between elements in thesimulator and steps in the actual printing process, described in thereferenced copending application. A disadvantage of this embodiment,however, is that it requires the inclusion of a separate nonlinearamplifier in the analog processor, thus increasing its cost.

FIG. 2 illustrates an embodiment of the invention in which aninexpensive modification to the ink-spread simulator presently employedin the analog processor of the copending application, provides amodified analog processor capable of simulating letterpress opera tion.In FIG. 2 input amplifier 18, nonlinear network 19 and output amplifier20, together comprise the inkspread simulator disclosed in the copendingapplication, and have a nonlinear transfer characteristic such as thatillustrated in FIG. 3, which simulates the typical ink-spreadingnonuniformity that occurs in offset type printing processes. However,the modified ink-spread simulator 14' of FIG. 2 also includes transistor21, diodes 22 and 28, and resistors 23-27 inclusive. This circuitryintroduces additional nonlinearity into the transfer characteristic ofthe ink-spread simulator, thereby to also simulate the dot etch losswhich occurs in the letterpress plate-makingprocess. The resultingmodifled transfer characteristic is illustrated in FIG. 4.

Briefly, the circuitry consisting of components 21-27 functions asfollows. Diode 22 initially is in a conducting state, preventing currentflow into nonlinear network 19 and thus preventing an output signaluntil the voltage on the cathode of diode 22 rises to a predeterminedvalue. This value is governed by the voltage at the emitter oftransistor 21, which in turn is controlled by the values of resistors 23through 27 and the two diodes 28. Thus, as the voltage of the inputsignal increases to rise, no output occurs (other than than caused byleakage through the diode 22) until a predetermined input signal voltageis reached, at which time diode 22 stops conducting. As the input signalvoltage continues to increase, the output signal voltage will increasein accordance with the nonlinear transfer characteristic of network 19.

Thus, signal processing element 14 is capable of simultaneouslysimulating both the dot etch loss of letterpress plate-making and theink-spread nonuniformity which occurs in all printing processes. Sincethis is an extremely simple and inexpensive modification to existinganalog processors, it is highly desirable. As in the FIG. 1 embodi-ment,it would be a simple matter to provide a by-pass switch for the addedcircuitry in FIG. 2 so that both offset and letterpress printingprocesses can be simulated.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention and it is, therefore, aimedto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. In a graphic arts process simulator having an analog signal processorwherein there is processed an electrical signal representative of thehalftone transparency from which a printing plate is made, an improvedanalog signal processor capable of simulating a letterpress graphic artsprocess wherein said improvements comprises:

a signal processing element responsive to said electrical signal andhaving a transfer characteristic proportional to the dot etch loss whichnormally occurs when letterpress printing plates are made.

2. In a graphic arts process simulator having an analog signal processorwherein there is processed an elecnormally occurs when letterpressprinting plates are made.

3. Apparatus in accordance with claim 2 wherein said modified signalprocessing element comprises a nonlinear amplifier whose transfercharacteristic simulates said ink spreading nonuniformities and whichfurther includes a diode for altering said transfer characteristic by anamount which corresponds to and therefore simulates the dot etch loss.

1. In a graphic arts process simulator having an analog signal processorwherein there is processed an electrical signal representative of thehalftone transparency from which a printing plate is made, an improvedanalog signal processor capable of simulating a letterpress graphic artsprocess wherein said improvements comprises: a signal processing elementresponsive to said electrical signal and having a transfercharacteristic proportional to the dot etch loss which normally occurswhen letterpress printing plates are made.
 2. In a graphic arts processsimulator having an analog signal processor wherein there is processedan electrical signal representative of a halftone transparency fromwhich a printing plate is made and which includes a signal processingelement that simulates ink spreading nonuniformities which normallyoccur in the printing process, an improved analog signal processorcapable of simulating a letterpress graphic arts process wherein saidimprovement comprises: a modified signal processing element responsiveto said electrical signal and having a transfer characteristic that isjointly proportional to said ink spreading nonuniformities and dot etchloss which normally occurs when letterpress printing plates are made. 3.Apparatus in accordance with claim 2 wherein said modified signalprocessing element comprises a non-linear amplifier whose transfercharacteristic simulates said ink spreading nonuniformities and whichfurther includes a diode for altering said transfer characteristic by anamount which corresponds to and therefore simulates the dot etch loss.